Separation of hydrocarbons



yatented Nov. 6, 1945 SEPARATION OF HYDROOARBONS Art 0. MoKlnnis, LongBeach, Calif., asslgnor to Union Oil Company of California, Los Angeles.Calif a corporation of California No Drawing. Application February 22,1943, Serial No. 476,771

13 Claims.

This invention relates to the preparation of pure hydrocarbons frompetroleum fractions or, more particularly, from narrow boiling fractionsof petroleum. More specifically it. relates to a method of treatment ofa complex hydrocarbon mixture to cause the separation of relativelyunsaturated or oleflnic hydrocarbons or of aromatic hydrocarbons fromrelatively saturated or paraffinic hydrocarbons or from naphthenichydrocarbons.

An object of the present invention is to provide a means of separatingindividual hydrocarbons from mixtures of hydrocarbons having boilingpoints so close as to prevent separation by means of ordinarydistillation processes. The method is less complex and involves fewersteps than chemical methods of separation and yields a purer productthan that produced by processes involving extraction with selectivesolvents.

Another object of the invention is to separate one Or more hydrocarbonsor classes of hydrocar. bons, such as paraiiins, olefins, diolefins andaromatics, which hydrocarbons have approximately the same boilingtemperature, from a petroleum fraction containing two or more differentclasses of hydrocarbons, said petroleum fraction being normally gaseousor normally liquid and preferably having a narrow boiling range.

A particular object of the invention is to separate relatively olefinichydrocarbons from relatively non-oleflnic hydrocarbon havingapproximately the same boiling point range and particularly to separatethe dioleflns from monoolefins and parafllns in the case of relativelynarrow boiling fractions containing these hydrocarbons, said fractionsbeing those such as may be obtained by the fractional distillation ofthe products of petroleum cracking or dehydrogenation processes.

It is also an object of my invention to separate aromatic hydrocarbonsfrom non-aromatic hydrocarbons having approximately the same boilingpoints or boiling point range.

The ditllculty in separating hydrocarbons having similar boiling pointsis well recognized and many methods have been suggested which include,in addition to chemical methods which are usually costly anduneconomical, the use of highly emcient fractional distillationprocesses,

solvent extraction processes and combinations of solvent extractionprocesses and distillation processes which in some instances may bedescribed as vapor phase solvent extraction processes. These processesare rather inefficient and uneconomical. On the other hand, processesinvolving the distillation of the hydrocarbon fraction in the presenceof compounds which form minimum boiling azeotropes with certain of theseparation of relatively pure hydrocarbons with high yields. The presentinvention relates to an improvement in an azeotropic distillationprocess.

According to my invention the separation of a specific hydrocarbon orhydrocarbon fraction from a mixture of hydrocarbons having substantiallythe same boiling range is accomplished by azeotropic distillation usingas an azeotrope former an organic nitrite having the general formulaRO--N=0 in which R is an alkyl radical. The addition of the azeotropeformer. i. e., the organic nitrite, to the petroleum fraction has theeffect of forming an azeotrope with certain of the hydrocarbons orhydrocarbon components, the azeotrope having a lower boiling point orrange than its hydrocarbon component or than the hydrocarbons which donot form azeotropes under the conditions of the distillation. Fractionaldistillation of the petroleum fraction containing the azetrope formerresults in the distillation of certain components or classes ofcomponents contained in the hydrocarbon fraction together with theazeotrope former at a temperature lower than the boiling point of thedistilled hydrocarbons. Such mixtures of distilled hydrocarbons andazeotrope former are referred to as minimum boiling azeotropes. Theother component or classes of components which do not form azeotropeswith the azeotrope former remain as a distillation residue.

Thus where it is desired to separate relatively oleflnic hydrocarbons,which fOr the purposes of this description will include diolefins, fromrelatively non-oleflnic hydrocarbons which likewise will includemonoolefins and parafiins, the narrow boiling range complex hydrocarbonmixture to which is added as appropriate amount of an azeotrope formeris fractionally distilled. The relatively non-oleflnic component formsazeotropes with the organic nitrite and may be distilled leaving as aresidue or bottoms the relatively oleflnic component which generallydoes not form an azeotrope with the organic nitrite. More specificallyin separating, for example, diolefins from monoolefins and paraffins anappropriate amount of a suitable organic nitrite is added to the complexhydrocarbon mixture and upon fractional distillation the azeotropesformed between the organic nitrite and parafllns and the 0 monoolefinsvaporize at temperatures below the boiling point of the dioleflns andare obtained as distillate and the diolefinic hydrocarbon material maybe obtained as a residue relatively free of parafiinlc and monoolefinicimpurities.

In practicing my invention it may be desirable in some cases to effectthe separation and isolation of three or more components originallypresent in a petroleum fraction. Thus in the case of the fractionreferred to above containing parafhydrocarbons in the mixture haveresulted in the fins, monoolefins and diolefins the separation of thethree components may be accomplished by adding an azeotrope former andcarefully fractionating and segregating the distillate. The paraffincomponent forms the lowest boiling azeotrope and will, therefore, be thefirst to distill. The monoolefln component which also forms anareotrope, then distills and leaves the diolefln component as a residue.This latter component may then be distilled if desired and thusseparated by fractional distillation from any remaining azeotropeformer.

Separation of the three aforementioned hydrocarbon components may beaccomplished more effectively by adding thereto Just sufilcientazeotrope former to form an azeotrope with the paraffin component andthe mixture distilled until all of the paraflins have been vaporized andremoved from the mixture of monooleflns and dioleflns remaining as aresidue. By this means it is possible to make a relatively sharpseparation because of the greater spread existing between the boilingrange of the paraffin azeotrope and that of the monoolefin componentthan between the boiling range of the paraflln azeotrope and themonoolefln azeotrope. After removal of the paraffin component anadditional quantity of azeotrope former is added which is Justsuflicient to form an azeotrope with the monoolefln component. Furtherdistillation results in the separation of the monoolefin as anazeotropic distillate and leaving the diolefln as a distillation bottomsor residue.

Thus by controlling the temperature and amount of azeotrope former, theazeotropic distillation may be controlled to distill overhead either theparailins alone or a mixture of parafllns and monooleflns, leaving thediolefins as a distillation residue.

While the inventilon is adapted to the separation of hydrocarbonfractions into hydrocarbon components having characteristics differentfrom each other, I have found that this process is particularlyadaptable to the separation of butadiene in a relatively pure form fromcracked or dehydrogenated petroleum fractions. The separation andrecovery of butadiene from the products of cracking of petroleumfractions or from dehydrogenated petroleum fractions is particularlydifficult. By straight distillation of certain cracked petroleumproducts it is possible to obtain a fraction containing 50 to 60% byvolume of butadiene and correspondingly 50 to 40% by volume ofpredominately C4 hydrocarbons consisting primarily of the parafllnic andmonoolefinic types. However, due to the rather close boiling points ofthese compounds, 1. e., from a 12" C. for isobutane to a +3.7" C. forcis butene-Z, it is not commercially feasible to make a completeseparation of these hydrocarbons by straight distillation processes. Itis particularly difficult to separate butadiene from this mixture ofhydrocarbons by fractional distillation because its boiling point, whichis a 4.7 0., falls approximately in the middle of the boiling pointrange of the C4 hydrocarbon fraction. Moreover, butadiene forms aminimum boilin point azeotrope with normal butane thus effectivelypreventing its separation by ordinary distillation methods.

In carrying out my invention I have found that the alkyl nitrites areexcellent azeotrope formers and those nitrites boiling between about 16C. and 175 C. and including the normal and the various isomeric alkylnitrites from methyl to octyl nitrite are particularly useful. Theparticular organic nitrite to be used for the treatment of a givenhydrocarbon fraction is selected on the basis of its boiling point. Thusthe azeotrope former will desirably have a boiling point at orrelatively near the average boiling point of the hydrocarbon fraction tobe treated. For example, the organic nitrite will desirably have aboiling point within 25 C. above to 50 C. below the average boilingpoint of the hydrocarbon fraction and preferably it will have a boilingpoint within 10 C. above to 30 C. below the average boiling point of thehydrocarbon stock.

When separating the hydrocarbon components of a C4 fraction of crackedpetroleum having an average boiling point of about a -4 C. and which maybe described as a butadiene fraction I may use either the methyl nitrite(boiling point about 16 C.) or the ethyl nitrite (boiling point 17 C.)although the use of the methyl nitrite is preferable. Similarly intreating a Ca fraction of cracked petroleum having an average boilingpoint of approximately 65 C. any of the propyl 0r butyl nitrites ormixtures of these nitrites might be used as the azeotrope formersalthough I prefer to employ one of the propyl nitrites. The boilingpoint of normal propyl nitrite is 57 C. or 8 C. below the averageboiling point of the above mentioned Ca fraction.

' As indicated above, the proportion of azeotrope former to be used maybe varied over wide limits and will depend upon the composition of thehydrocarbon fraction, the efliciency of the operation, the desiredpurity of the product, and the technique to be used in the distillation.For example, in separating parafllns from monoolefins, both of whichform azeotropes with added azeotrope forming agent, it is desirable toadd a quantity of the azeotrope former which will distill completelywith the paramns and which will cause the complete removal of theparainns. The addition of a quantity less than this specified amountwill leave some of the paraflins in the oleflnic distillation residue.The addition of more than the specified amount will form an azeotropewith the olefins thus bringing the distillation temperature of theoleflns nearer to that of the parafiln azeotrope and making theseparation of these two components more difflcult.

In separating the relatively oleflnic hydrocarbons from the relativelynon-olefinic hydrocarbons, such as for example in separating butadienefrom the butenes and the butanes present in a closely fractionated C4fraction of cracked petroleum, the amount of azeotrope former to be usedis not as critical as in the above-described example. In this instancethe butadiene does not form an azeotrope with for example methyl nitriteso that although it i desirable to use sunlcient azeotrope former todistill all of the relatively non-olefinic components an excess of theazeotrope former may be employed. When using methyl nitrite as theazeotrope former any excess methyl nitrite remaining after the completeremoval of the paraflinic and monoolefinic com- .ponents may bedistilled leaving the butadiene as a residue.

The pressures employed in carrying out the azeotropic distillation usingan organic nitrite as the azeotrope former may vary from substantiallyzero, 1. e., from 1 to 2 mm. of mercury pressure, to pressures of 300pounds per square inch absolute or even higher, although I prefer tooperate between about 15 mm. of mercury pressure and about pounds persquare inch and in some instances, particularly when treating the lowermolecular weight hydrocarbon fractions, the preferred pressure rangewill bein the order of from normal atmospheric pressure to 200 poundspersquare inch absolute. The pressure employed will depend upon theparticular hydrocarbon fraction being treated and upon the particular.organic nitrite being used as the azeotrope former as well as upon theseparation desired and upon various economic considerations. It is knownthat the composition as well as the boiling point or range of azeotropescomprising hydrocarbons and organic nitrites will vary with changes inpressure. In general the higher the pressure the higher will be theratio of hydrocarbon to organic nitrite in a given azeotrope althoughthe relative efiects of pressure upon the boiling points of varioushydrocarbon components are not constant and it may be advantageous insome instances to employ the higher pressures in order to obtain agreater spread between the boiling points or the azeotropes of thevarious hydrocarbon components. In distilling unsaturated andparticularly relatively olefinic petroleum fractions it is preferablethat distillation temperatures be employed which are not high enough tocause polymerization of the more olefinic hydrocarbons. Sincedistillation temperature is a function of pressure and increases with anincrease in pressure it is apparent that there is a maximum allowablepressure for the treatment of a given hydrocarbon fraction and thismaximum pressure will depend upon the relative ease with whichpolymerization occurs in the hydrocarbon fraction. In general, however,economic considerations make it preferable to operate at or relativelynear atmospheric pressure or in the lower pressure ranges hereinbeforeindicated.

The azeotrope, produced as an overhead in an azeotropic distillation isseparated into its components, i. e., azeotrope former and hydrocarbon,by adding a third component which is soluble in the azeotrope former orwhich dissolves the azeotrope former and which causes phase separationor stratiflcation of the azeotrope. The quantity of the said thirdcomponent, which will be hereinafter referred to as solvent, to be usedwill be that amount required to effect a substantially completeseparation of the hydrocarbon component as one phase and the azeotropeformer and the solvent as a second phase. The phases are separated bydecantation and the hydrocarbon phase may be contacted and/or extractedone or more times with fresh portions of the said solvent to removecompletely any azeotrope former which may remain in the said hydrocarbonfraction. The phase comprising the azeotrope former and solvent isseparated by fractional distillation and the pure azeotrope former maybe returned to the azeotrope distillation step for reuse.

Substances which may be used as solvents to effect the desired phaseseparation of an azeotrope comprising hydrocarbon material and organicnitrite include water, the lower molecular weight aliphatic alcohols andglycols, and glycerol. Of the alcohols I prefer to use methanol,ethanol, the propanols, and the butanols, and of the glycols, ethyleneglycol and propylene glycol, although I may in certain instances usehigher molecular weight alcohols and glycols. While I may use any or allthese substances I prefer to use water alone or mixtures of water withone or more of the said alcohols, glycols or glycerol. The particularratio of water to alcohol or glycol, or glycerol to be used will dependupon the specific azeotrope being treated, i. e., upon thehydrocarrelatively miscible with the organic nitrite.

4 water.

bon or hydrocarbon component as well as upon the nitrite, and itwill'also depend upon the process to be employed in recovering theazeotrope former.

The] separation of the azeotr ape may be considered to be a solventextraction process in which the azeotrope former-is selectivelyextracted from the hydrocarbon component by means of a. solvent, thesolvent being relatively immiscible with the hydrocarbon component andThe solvent extraction process may be carried out as a batch operation,as hereinbefore described, or

it may be efl'ected by any at all of the general-' methods well known'tothose skilled in the art, such as for example, it may be carried out ina continuous countercurrent extractor in which the azeotrope enters anextraction column at a point near its base and flows countercurrent tothe solvent which enters the column at a point near the top. In itsdownward flow the solvent contacts the rising azeotrope and/or partiallyextracted azeotrope and selectively dissolves the azeotrope former. Thepure hydrocarbon component is produced at the top of the column and thesolvent containing azeotrope former but free from hydrocarbon is drawnfrom the bottom of the column.

Separation of the mixture of solvent and azeotrope former' is thenaccomplished by fractional distillation and the method of carrying outthis separation will depend upon the particular nitrite employed andupon the particular solvent used for its recovery. A mixture of solventand azeotrope former, obtained by extraction of an azeotrope produced inthe separation of a C4 fraction of cracked petroleum, might consist ofmethyl nitrite, methanol and water, a mixture of the latter twocompounds having been used as the solvent for treating the azeotrope. Inthis instance the methyl nitrite could be separated in a pure form fromthe alcohol-water solvent by a simple topping distillation, the methylnitrite being obtained as a distillate at about l6 C. leaving as aresidue the mixture of alcohol and In the distillation of a mixture ofisopropanol, water and normal hexyl nitrite obtained by the extractionof an azeotrope produced in the separation of a petroleum fractionhaving an average boiling point of about 140 C. the alcohol and waterdistill first leaving the hexyl nitrite as a residue. The nitrite may bewithdrawn from the still without further treatment or the distillationmay be continued and the nitrite recovered as a distillation fraction.

The foregoing azeotropic distillation process is also applicable to theseparation of aromatic hydrocarbons from non-aromatic hydrocarbons, suchas paraifins, naphthenes or olefins or mixtures thereof. Thus apetroleum fraction containing aromatics whose boiling range includesthat of the aromatic compound to be isolated, for instance C. to C. fortoluene, (suitable other temperature ranges for fractions containingbenzene or dior other polyalkyl benzenes) may be distilled with anorganic nitrite or a mixture of organic nitrites having a boiling pointin the aforementioned desired boiling range. The non-aromatichydrocarbon components form azeotropes with the organic nitrite anddistill first leaving the aromatic hydrocarbon as a residue. I

My invention is further illustrated by the following examples:

. In carrying out the separation of butadiene fractionated C4 fractionof cracked petroleum according to the principles of my invention, to 100parts of the C4 fraction containing approximately 50 parts by weight ofbutadiene, 40 parts by weight of butene-l and isobutene and parts byweight of butanes is added approximately 130 parts by weight or methylnitrite and the resulting mixture is distilled under ordinaryatmospheric pressures. The first produced distillate is the butaneazeotrope which vaporizes at between 20" C. and -17 C. The azeotropecontaining butenel and isobutene is then distilled at about -16 C.followed by any remaining methyl nitrite which vaporizes atapproximately the same temperature. The distillation temperature risesabruptly to approximately 4.'7 C. when relatively pure butadiene isproduced as a distillate.

In another example, to 100 parts of the above mentioned closelyfractionated C4 fraction of cracked petroleum is added 20 parts byweight of methyl nitrite and the mixture is distilled under ordinaryatmospheric pressure until the added component has substantially alldistilled at which time the temperature which has been in the order of-20 C. to l'l C. abruptly begins to rise. The azeotropic distillate isextracted with a solvent to separate and recover the methyl nitrite andthe hydrocarbon component separated consists primarily of butanes. Anadditional 110 parts of methyl nitrite is then added to the residue fromthe above distillation which comprises a mixture of butene-l, isobuteneand butadiene. The distillation is continued until the temperature whichhas been in the order of l6 C. again rises abruptly indicating that allof the butene-l azeotrope, isobutene azeotrope and excess azeotropeformer has been distilled over leaving relatively pure butadiene as adistillation residue. This azeotrope is then treated to separatetherefrom the monoolefin hydrocarbon components and the azeotropeformer. If the distillation resi.. due contains relatively small amountsof higher boiling hydrocarbons which were originally present in thehydrocarbon fraction or which formed during the azeotropic distillationthe distillation may be continued without further addition of methylnitrite to produce as a distillate a relatively pure butadiene leavingthe impurities as a distillation residue.

The treatment of a C4 fraction of cracked petroleum containingapproximately 60 parts by weight of butadiene, 10 parts by weight ofbutene-2s, 20 parts by weight of butene-l and isobutene and 10 parts byweight of butanes is effected by combining 100 parts by weight of the C4fraction with 70 parts by weight of methyl nitrite and distilling theresulting mixture at ordinary atmospheric pressures. The distillationtemperature rises slowly from about 20 C. when the butane azeotropestarts to distill to about 16 C.

When all of the methyl nitrite, butanes, butenel and isobutene havedistilled the distillation temperature rises abruptly to approximately4.'7 C. at which temperature the relatively pure butadiene distillsleaving butene-2 as a residue.

In the treatment of a butadiene fraction containing approximately 70parts by weight of butadiene, 20 parts by weight of butene-l and 10parts by weight of isobutene, the said butadiene fraction is mixed withan equal weight of methyl nitrite and the mixture is distilled underordinary atmospheric pressures. The azeotrope containing the butenesvaporizes at about l6 C. and distills first and the excess methy1nitrite then distills at approximately the same temperature leaving therelatively pure butadiene as a residue.

The foregoing description is not to be taken as in any way limiting butmerely as illustrative of my invention for many variations may be madeby those skilled in the art without departing from the spirit or scopeof the following claims:

I claim:

1. A method for the treatment of a complex hydrocarbon fraction toseparate chemically similar components from other chemically similarcomponents, diflerent from said first named chemically similarcomponents contained in said complex hydrocarbon fraction, whichcomponents distill from said complex hydrocarbon fraction atapproximately the same temperature, which comprises distilling saidcomplex hydrocarbon fraction in the presence of a sufllcient amount ofan alkyl nitrite to vaporize chemically similar components together withsaid alkyl nitrite. thereby leaving chemically similar componentsdifferent from said vaporized chemically similar components in the'residue, said alkyl nitrite having a boiling point within 25 C. aboveto 50 C. below the average boiling point of the said complex hydrocarbonfraction.

2. A method for the treatment or a complex hydrocarbon fraction toseparate chemically similar components from other chemically similarcomponents, different from said first named chemically similarcomponents contained in said complex hydrocarbon fraction, whichcomponents distill from said complex hydrocarbon fraction atapproximately the same temperature, which comprises distilling saidcomplex hydrocarbon fraction in the presence of a sufllcient amount ofan alkyl nitrite to vaporize chemically similar components together withsaid organic nitrite,

40 thereby leaving chemically similar components diiferent from saidvaporized chemically similar components in the residue, said alkylnitrite containing from 1 to 8 carbon atoms in the organic radical.

3. A method for the treatment of a complex hydrocarbon fraction toseparate chemically similar components from other chemically similarcomponents, different from said first named chemically similarcomponents contained in said complex hydrocarbon fraction, whichcomponents distill from said complex hydrocarbon fraction atapproximately the same temperature, which comprises distilling saidcomplex hydrocarbon fraction, under pressures in the order of from 0 to300 pounds per square inch absolute in the presence of a sufficientamount of an alkyl nitrite to vaporize chemically similar componentstogether with said alkyl nitrite, thereby leaving chemically similarcomponents different from said vaporized chemically similar componentsin the residue, said alkyl nitrite containing from 1 to 8 carbon atomsin the organic radical and having a boiling point within 25 C. above to50 C. below the average boiling point of the said complex hydrocarbonfraction.

4. A method for the treatment of an oleflnic hydrocarbon fraction toseparate relatively olefinic hydrocarbons from relatively non-olefinichydrocarbons which distill from said olefinic hydrocarbon fraction inthe same temperature range as said relatively non-olefinic hydrocarbonsdistill therefrom which comprises distilling said olefinic hydrocarbonfraction in the presence of a sufficient amount of an alkyl nitrite todistill said relatively non-olefinic hydrocarbons together with saidalkyl nitrite thereby leaving said relatively olefinic hydrocarbons inthe residue substantially completely separated from said relativelnon-olefinic hydrocarbons, said alkyl nitrite having a boiling pointwithin 25 C. above to 50 C. below the average boiling point of saidolefinic hydrocarbon fraction.

5. A method for the treatment of an olefinic hydrocarbon fraction toseparate relatively olefinic hydrocarbons from relativel non-olefinichydrocarbons which distill from said olefinic hydrocarbon fraction inthe same temperature range as said relatively non-olefinic hydrocarbonsdistill therefrom which comprises distilling said olefinic hydrocarbonfraction, under absolute pressures in the order of from to 300 poundsper square inch, in the presence of a suincient amount of an alkylnitrite to distill said relatively non-olefinic hydrocarbons togetherwith said alkyl nitrite thereby leaving said relatively olefinichydrocarbons in the residue substantially completely separated from saidrelatively non-olefinic hydrocarbons, said alkyl nitrite having aboiling point within 25 C. above to 50 C. below the average boilingpoint of said olefinic hydrocarbon fraction.

6. A method for the treatment of an olefinic hydrocarbon fractiontoseparate relatively olefinic hydrocarbons from relatively non-oleflnichydrocarbons which distill from said olefinic hydrocarbon fraction inthe same temperature range as said relatively non-olefinic hydrocarbonsdistill therefrom which comprises distilling said olefinic hydrocarbonfraction, under absolute pressures in the order of from mm. of mercuryto 100 pounds per square inch, in the presence of a sufficient amount ofan alkyl nitrite to distill said relatively non-olefinic hydrocarbonstogether with said alkyl nitrite thereby leaving said relativelyolefinic hydrocarbons in the residue substantially completely separatedfrom said relatively non-olefinic hydrocarbons, said alkyl nitritecontaining from 1 to 8 carbon atoms in the alkyl radical and having aboiling point within C. above to 50 C. below the average boiling pointof said oleflnic hydrocarbon fraction.

7. A method for the treatment of a hydrocarbon fraction containing C4paraflln, monoolefin and diolefin hydrocarbons to separate the diolefinhydrocarbon from the monoolefin and paraflin hydrocarbons which distillfrom the said hydrocarbonfraction in the same temperature range as thediolefin hydrocarbon distills therefrom, which comprises distilling saidhydrocarbon fraction in the presence of sufficient alkyl nitrite tovaporize the monoolefin and paraflin hydrocarbons together with thealkyl nitrite thereby leaving the diolefin hydrocarbon in the residuesubstantially completely separated from the hydrocarbons other thandiolefin hydrocarbons, said alkyl nitrite having a boiling point within25 C. above to 50 0. below the average boiling point of said hydrocarbonfraction,

8. A method for the treatment of a butadiene fraction containinghydrocarbons other than butadiene which distill from said butadienefraction in the same temperature range as said butadiene distillstherefrom which comprises distilling said butadiene fraction, under apressure in the order of from normal atmospheric pressure to 200 poundsper square inch absolute in the presence of a suiiicient amount of analkyl nitrite to vaporize said hydrocarbons other than butadienetogether with said alkyl nitrite, thereby leaving butadiene in theresidue substantially completely separated from said hydrocarbons otherthan butadiene, said alkyl nitrite having a boiling point within 25 C.above to 50 C. below the average boiling point of the butadienefraction.

9. A method for the treatment of a hydrocarbnn fraction containing thebutanes, butene-l, isobutene, and butadiene, to separate butadienetherefrom which comprises distilling said hydrocarbon fraction in thepresence of suflicient methyl nitrite to vaporize the butanes and thebutenes together with the methyl nitrite thereby leaving the butadieneas a residue substantially completely separated from butanes,-butene-1and isobutene.

10. A method for the-treatment of a hydrocarbon fraction containingbutene-l, isobutene and butadiene, to separate butadiene therefrom whichcomprises distilling said hydrocarbon fraction under pressures in theorder of from about normal atmospheric pressure to about 200 pounds persquare inch absolute, in the presence of sufficient methyl nitrite tovaporize the butenes together with the methyl nitrite thereby leavingthe butadiene as a residue substantially completely separated frombutene-l and isobutene.

11. A method for the treatment of a butadiene fraction of petroleumcontaining butanes, isobutene, butene-l, and the butene-2s to separatebutadiene therefrom which comprises distilling said butadiene in thepresence of a suflicient amount of methyl nitrite to vaporize thebutanes, isobutene, and butene-l, together with the methyl nitrite,thereby leaving a distillation reeldue containing butadiene and thebutene-Zs substantially completely separated from the butanes, isobuteneand butene-l.

12. A method for the treatment of a butadiene fraction of petroleumcontaining butanes, isobutene, butene-l, and the butene-2s to separatebutadiene therefrom which comprises distilling said butadiene in thepresence of a sufficient amount of methyl nitrite to vaporize thebutanes, isobutene, and butene-l, together with the methyl nitrite,thereby leaving a distillation residue containing butadiene and thebutene-2s substantially completely separated from th butanes, isobuteneand butene-l and subsequently separating said butene-2s from saidresidue of butene-2s and butadiene.

13. A method for the treatment of a butadiene fraction of petroleumcontaining butanes, isobutene, butene-l, and the butene-2s to separatebutadiene therefrom which comprises distilling said butadiene fractionin the presence of a sufflcient amount of methyl nitrite to vaporize thebutanes, isobutene, and butene-l, together with the methyl nitrite,thereby leaving a distillation residue containing butadiene and thebutene-2s substantially completely separated from the butanes, isobuteneand butene-l and subsequently distilling the said distillation residueto distill the butadiene substantially completely separated from thebutene-2s thereby leaving the butene-2s as a residue.

' ART 0. McKlNNIS.

